Differing boost voltages applied to two or more anodeless electrodes for plasma processing

ABSTRACT

This disclosure describes a non-dissipative snubber circuit configured to boost a voltage applied to a load after the load&#39;s impedance rises rapidly. The voltage boost can thereby cause more rapid current ramping after a decrease in power delivery to the load which results from the load impedance rise. In particular, the snubber can comprise a combination of a unidirectional switch, a voltage multiplier, and a current limiter. In some cases, these components can be a diode, voltage doubler, and an inductor, respectively.

CLAIM OF PRIORITY UNDER 35 U.S.C. §120

The present application for patent is a Continuation in Part of patentapplication Ser. No. 13/666,668 entitled “ADJUSTABLE NON-DISSIPATIVEVOLTAGE BOOSTING SNUBBER NETWORK” filed Nov. 1, 2012, pending, andassigned to the assignee hereof and hereby expressly incorporated byreference herein.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to power supplies. Inparticular, but not by way of limitation, the present disclosure relatesto systems, methods and apparatuses for limiting voltage and currentspikes in a power supply.

BACKGROUND

FIG. 1 illustrates one example of a typical power supply system 100 usedfor plasma processing. The power supply system 100 includes a DC powersupply 102 providing DC power to a switching circuit 104 that convertsthe DC power into pulsed DC and provides the pulsed DC to a plasma load106. When switching, the potential between nodes C and D passes througha potential of zero, and the plasma can be extinguished or can dim to anextent that it becomes highly resistive and acts like an unfluxedinductor or an open circuit for a short time after this transition.Immediately after this transition, the DC power supply 102 continues toprovide power to the switching circuit 104, but most of that power canno longer be delivered to the plasma load 106. Instead, the powerpredominantly passes through the switching circuit 104 potentiallydamaging the switching circuit 104.

A snubber 108 can be used to mitigate damage to the switching circuit104 by absorbing power from the DC power supply 102 during the periodafter the switching circuit 104 transitions through 0 V. However,existing snubbers are typically dissipative snubbers and/or dissipatesignificant power.

Additional challenges to known power supply systems include slowprocessing throughput and further inefficiencies from power dissipation.For instance, and as seen in FIG. 2A, while voltage between nodes C andD can switch with negligible ramp time, current ramps at a much slowerpace thus providing an average power that is significantly lower thanthe power output from the DC power supply 102. This leads to longerprocessing periods and decreased throughput, since many processes canonly end when a predetermined total power has been delivered.

There is also a desire to increase DC pulse frequency provided to theplasma load 106 since this reduces arcing. However, the above-notedproblems become more acute at higher frequencies, as illustrated in FIG.2B. Furthermore, since each pulse is shorter at higher frequency, thecurrent at high frequency may end up larger (in a power-regulatedsystem) than at lower frequency. Since power dissipation is proportionalto I², these larger currents lead to larger power losses. Additionally,switching losses, which are proportional to the current at the moment ofswitching, are accentuated at higher frequencies since switching currentis larger.

SUMMARY OF THE DISCLOSURE

Exemplary embodiments of the present invention that are shown in thedrawings are summarized below. These and other embodiments are morefully described in the Detailed Description section. It is to beunderstood, however, that there is no intention to limit the inventionto the forms described in this Summary of the Invention or in theDetailed Description. One skilled in the art can recognize that thereare numerous modifications, equivalents and alternative constructionsthat fall within the spirit and scope of the invention as expressed inthe claims.

Some embodiments of the disclosure may be characterized as a powersystem comprising a DC power supply, a switching circuit, and a snubbercircuit. The DC power supply can supply DC power to first and secondrails having a voltage between the first and second rails. The switchingcircuit can receive the DC power via the first and second rails andconverting the DC power to a pulsed DC voltage, the pulsed DC voltageconfigured for application to a plasma load. The snubber circuit can becoupled to the first and second rails such that the voltage between thefirst and second rails falls across the snubber circuit. Furthermore,the snubber circuit can comprise a first unidirectional switch, avoltage multiplier, an electrical node, and a current limiter. The firstunidirectional switch can be configured to allow current to pass fromthe first rail. The voltage multiplier can be coupled between the firstunidirectional switch and the second rail. The voltage multiplier can beconfigured to absorb and store energy from the DC power supply via thefirst unidirectional switch when an impedance seen by the switchingcircuit increases. It can also be configured to boost the voltagebetween the first and second rails by virtue of absorbing and storingthe energy from the DC power supply. It can further be configured tothen apply at least a portion of the stored energy to the switchingcircuit when the impedance seen by the switching circuit decreases andthereby decrease the voltage between the first and second rails. Theelectrical node can be arranged between the first unidirectional switchand the voltage multiplier. The current limiter can be coupled betweenthe electrical node and the first rail and can limit rises in currentthat the voltage multiplier discharges to the switching circuit

Other embodiments of the disclosure may also be characterized as asnubber circuit comprising a voltage multiplier, a first unidirectionalswitch, and a first current-limiter. The voltage multiplier can becoupled between a first power rail and a second power rail and it canabsorb and store energy from the first rail and consequently boost avoltage between the first and second rail, and then discharge at leastsome of the energy and consequently reduce the voltage between the firstand second rail. The first unidirectional switch can allow current topass from the first power rail to the voltage multiplier, but can blockcurrent attempting to pass back to the first power rail through thefirst unidirectional switch. The first current-limiter can be coupledbetween the first power rail and the voltage multiplier. The firstcurrent-limiter can provide a low-resistance current path from thevoltage multiplier to the first power rail and can limit a rate ofchange of current that the voltage multiplier discharges to the firstpower rail.

Other embodiments of the disclosure can be characterized as a methodcomprising passing power from a power supply to a load having animpedance. The method can also include absorbing at least some of thepower when the impedance of the load substantially increases and therebyincreasing a voltage and a current reaching the load. The method finallyincludes discharging at least some of the absorbed power into the loadwhen the impedance of the load decreases, such that the discharge issubstantially non-dissipative.

BRIEF DESCRIPTION OF THE DRAWINGS

Various objects and advantages and a more complete understanding of thepresent invention are apparent and more readily appreciated by referringto the following detailed description and to the appended claims whentaken in conjunction with the accompanying drawings:

FIG. 1 illustrates one example of a typical power supply system used forplasma processing;

FIGS. 2A and 2B illustrate plots of voltage and current for atraditional power supply system;

FIG. 3 illustrates a power supply system including a DC power supply, aswitching circuit, a plasma load, and an embodiment of a non-dissipativesnubber circuit;

FIG. 4 illustrates a power supply system including a DC power supply, aswitching circuit, a plasma load, and another embodiment of adissipative snubber circuit;

FIG. 5 illustrates a power supply system including a DC power supply, aswitching circuit, a plasma load, and yet another embodiment of anon-dissipative snubber circuit;

FIG. 6 illustrates a power supply system including a DC power supply, aswitching circuit, a plasma load, and yet another embodiment of anon-dissipative snubber circuit;

FIG. 7 illustrates a power supply system including a DC power supply, aswitching circuit, a plasma load, and yet another embodiment of anon-dissipative snubber circuit;

FIGS. 8A and 8B illustrate plots of voltage and current for a powersupply system according to one embodiment of this disclosure;

FIG. 9 illustrates an embodiment of a power supply system showingdetails of a voltage multiplier;

FIG. 10 illustrates an embodiment where the voltage multiplier of thesnubber is a voltage tripler;

FIG. 11 illustrates a power supply system including a DC power supply, aswitching circuit, a plasma load, yet another embodiment of a snubbercircuit, and a voltage multiplier modifier;

FIG. 12 illustrates a plot of voltage and current for a power supplysystem according to one embodiment of this disclosure;

FIG. 13 illustrates a power supply system showing details of oneembodiment of a voltage multiplier modifier;

FIG. 14 illustrates a power supply system showing details of oneembodiment of a voltage multiplier and of a voltage multiplier modifier;

FIG. 15 illustrates a power supply system including a DC power supplyproviding power to a switching circuit, which then provides pulsed DCpower to a plasma load;

FIG. 16 illustrates a power supply system including a DC power supplyproviding power to a switching circuit, which then provides pulsed DCpower to a plasma load;

FIG. 17 illustrates a power supply system including a DC power supplyproviding power to a switching circuit, which then provides pulsed DCpower to a plasma load;

FIG. 18 illustrates the power supply system of FIG. 14 just after a 0 Vtransition of the switching circuit;

FIG. 19 illustrates the power supply system of FIG. 14 during a fallingedge of a voltage boost from the snubber;

FIG. 20 illustrates the current paths and diode biases in the powersupply system of FIG. 14 during a single arc event;

FIG. 21 illustrates the current paths and diode biases in the powersupply system of FIG. 14 during a succession of high-frequency arcs;

FIG. 22 illustrates another embodiment of a power supply system;

FIG. 23 illustrates yet another power supply system;

FIG. 24 illustrates yet a further power supply system;

FIGS. 25A and 25B illustrate plots of voltage and current for a powersupply system according to one embodiment of this disclosure;

FIG. 26 illustrates a method of controlling power in a power supplysystem; and

FIG. 27 shows a diagrammatic representation of one embodiment of amachine in the exemplary form of a computer system;

FIG. 28 illustrates an alternative topology for a voltage-boostingcircuit;

FIG. 29 illustrates another embodiment of a voltage boosting circuithaving snubber functionality; and

FIG. 30 illustrates an embodiment of a power supply system including twoor more pulsed DC power supply systems providing pulsed DC power to fouror more anodeless electrodes in a plasma processing chamber.

DETAILED DESCRIPTION

The present disclosure relates generally to power supply systems. Morespecifically, but without limitation, the present disclosure relates toa non-dissipative snubber for use in a power supply system.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments.

For the purposes of this disclosure, a current limiter is any device orcircuit that limits a current that can pass through the current limiteror that limits a rate at which current passing through the currentlimiter can rise or fall. In some embodiments, a current limiter canlimit both the rate of increase and an upper bound of the currentpassing through the current limiter. An inductor, resistor, JFET,MOSFET, and IGBT are all examples of current-limiting elements sinceeach are able to limit the rate of change of and amount of current.

For the purposes of this disclosure, a switch includes any circuit ordevice that stops the passage of current when in an off or open state.For instance, transistors (e.g., MOSFET, BJT, IGBT) can be a switch, andin some cases, where a current limiter is operated so as to reducecurrent to 0 A, a current limiter can be a switch.

For the purposes of this disclosure, a unidirectional switch includesany device or circuit that only passes current in a single direction.For instance, both a diode and a transistor can be considered aunidirectional switch, depending on operation.

The challenges noted in the background can be dealt with via use of anon-dissipative snubber 2460 as illustrated in FIG. 24, comprising afirst unidirectional switch 2410, a voltage multiplier 2418, and a firstcurrent limiter 2412. The snubber 2460 can be arranged between a firstpower rail 2450 and a second power rail 2452, wherein the power rails2450 and 2452 transfer power from a power supply 2402 to a load 2406(e.g., a plasma of a plasma processing chamber), and optionally transfersaid power through vulnerable circuitry 2404 (e.g., a switchingcircuit). The first unidirectional switch 2410 can be arranged between afirst power rail 2450 and the voltage multiplier 2418 and allows currentto pass from the first power rail 2450 to the voltage multiplier 2418(optionally through a current limiter 2408), but prevents current fromtraveling a reverse path through the unidirectional switch 2410. Thefirst current limiter 2412 can couple the voltage multiplier 2418 to thefirst power rail 2450 in parallel to the unidirectional switch 2410 andprovides a low-loss current path from the voltage multiplier 2418 to thefirst power rail 2450. The snubber 2460 may further include a switch2422 between the voltage multiplier 2418 and the first current limiter2412, wherein the switch 2422 remains closed during most operations, butis opened when a current in the current limiter 2412 reaches athreshold, and then closes when the current in the current limiter 2412falls below the threshold.

One advantage of the snubber 2460 is its ability to non-dissipativelyabsorb energy from the power supply 2402 when an impedance of the load2406 increases, or substantially increases. For instance, where the load2406 is a plasma, and the plasma dims or is extinguished, the plasmaimpedance increases substantially. When the load 2406 impedanceincreases substantially, the power supply 2402 continues to deliver thesame power, and this power would dissipate largely in the vulnerablecircuitry 2404. However, the snubber 2460, and in particular, thevoltage multiplier 2418, absorbs a large portion of this energy, thusprotecting the vulnerable circuitry 2404.

Another advantage of the snubber 2460 is to avoid rapid discharges ofthe stored energy in the voltage multiplier 2418 when the load 2406impedance suddenly drops. For instance, where the load 2406 is a plasma,and an arc in the plasma occurs, the arc creates a low impedance currentpath for the energy in the voltage multiplier 2418. However, the currentlimiter 2412 prevents rapid discharge of the voltage multiplier 2418. Inthe case of plasma arcs, this aspect helps prevent the snubber 2460 fromexacerbating arcs.

A third advantage of the snubber 2460 is an ability to boost a voltagethat the power supply 2402 provides to the load 2406, and consequentlyboosts a current ramp rate provided to the load 2406. When the voltagemultiplier 2418 absorbs energy from the power supply 2402, a voltageacross the voltage multiplier 2418 can be raised to some multiple of avoltage between nodes A and B, V_(AB), generated by the power supply2402. In this way, the voltage multiplier 2418 can boost a voltage, andthus a current ramp rate, provided to the load 2406 after the load 2406impedance rises. Where there is a desire to control or limit themultiplying effect of the voltage multiplier 2418, (e.g., where one ormore devices have a voltage threshold that can be exceeded if thevoltage multiplier's full effect is enabled) an optional voltagemultiplier modifier 2420 may be utilized (see FIGS. 11-14). The voltagemultiplier modifier acts as a ‘control knob’ over the voltage boostprovided by the voltage multiplier 2418.

The power supply 2402 can be embodied by a current source or othercurrent-regulating power supply. In one embodiment, the power supply2402 can be any power supply having an output current that is limited toslow changes in current. For instance, the power supply 2402 can be anypower supply having an inductive output behavior. The power supply 2402may be able to raise its compliance voltage, and hence the voltageV_(AB). The ability to raise the compliance voltage, and hence, V_(AB),can further enable turn-on of the unidirectional switch 2410.

The snubber 2460 has particular application to pulsed DC power systemsproviding pulsed DC power to a plasma load during plasma processing. Forinstance, and as illustrated in FIG. 7, a non-dissipative snubber can bearranged between a DC power supply 702 (e.g., power supply 2402) and aswitching circuit 704 (e.g., vulnerable circuitry 2404) providing pulsedDC voltage to a plasma load 706 (e.g., load 2406). In this application,the non-dissipative snubber absorbs power from the DC power supply 702when the plasma load 706 impedance rises such that power would otherwisedamage the switching circuit 704 (e.g., immediately after the switchingcircuit voltage transitions through 0 V), avoids excessive currentdischarge during arc events in the plasma, and increases a ramp rate ofcurrent provided to the plasma load 706 during each voltage pulse. Theseadvantages can be especially beneficial for high frequency pulsing andhigh power applications.

The non-dissipative snubber includes a voltage multiplier 724 thattemporarily boosts a voltage V_(AB) and thus a current provided to theswitching circuit 704 in order to increase an average power delivered tothe plasma load 706, thereby increasing throughput, and decreasinglosses from excessive currents. The non-dissipative snubber can alsoinclude an inductor 712 to prevent the voltage multiplier 724 fromrapidly discharging stored energy into the switching circuit 704 and theplasma load 706 when the plasma load 706 drops (e.g., during an arc).The snubber circuit may further include a switch 726 between the voltagemultiplier 724 and the inductor 712 to help stop runaway current rampingin the inductor 712 caused by high-frequency multiple arc events in theplasma (e.g., rapid succession of arcs). Various diodes 710, 714, and728 and capacitors can be interleaved with the above-noted components inorder to control the direction of currents in the non-dissipativesnubber and various capacitors can be used to store energy.

In one embodiment, a capacitor can replace the voltage multiplier 724(see FIG. 6). In one embodiment, the voltage multiplier 724 can be avoltage doubler (see FIG. 9), a voltage tripler (see FIG. 10), or anyother multiplier having an integer or fractional multiplying effect.

Before delving deeper into FIGS. 7 and 24, a discussion of thedevelopment of these circuits and power systems may be helpful. FIG. 3illustrates a power supply system 300 including a DC power supply 302, aswitching circuit 304, a plasma load 306, and an embodiment of anon-dissipative snubber circuit. The DC power supply 302 provides DCpower to the switching circuit 304 (e.g., a half-bridge switchingcircuit) which converts the DC power to pulsed DC that is then providedto the plasma load 306. In order to prevent damage to the switchingcircuit 304 during switching, when the plasma load 306 appears as acapacitor or open circuit, a snubber circuit including a capacitor 308coupled between a first rail 350 (positive rail) and a second rail 352(negative rail) can be implemented. While the capacitor 308 can limitcurrent and/or voltage spikes in the switching circuit 304, itunfortunately also quickly discharges stored energy into arcs in theplasma, thus exacerbating such events.

FIG. 4 illustrates a power supply system 400 including a DC power supply402, a switching circuit 404, a plasma load 406, and another embodimentof a dissipative snubber circuit. In this embodiment the snubber circuitincludes a diode 410, a capacitor 408, and a resistor 412. Duringswitching circuit 404 switching, when the plasma load 406 appears as acapacitor or open circuit, a majority of power from the DC power supply402 passes through the diode 410 and charges the capacitor 408. Thecapacitor 408 can discharge its energy through the resistor 412 to theswitching circuit 404 in the plasma load 406 when the plasma load 406impedance returns to typical levels. Unlike the snubber illustrated inFIG. 3, the snubber of FIG. 4 limits the current that the capacitor 408discharges to the first rail 450 via the resistor 412, whose resistancecan be selected to meet a maximum current threshold. However, power isdissipated as current passes through the resistor 412, and thus thisdesign is merely a dissipative snubber.

FIG. 5 illustrates a power supply system 500 including a DC power supply502, a switching circuit 504, a plasma load 506, and yet anotherembodiment of a non-dissipative snubber circuit. However this designreplaces the resistor 412 in FIG. 4 with an inductor 512, thus enablingthe capacitor 508 to discharge stored energy in a non-dissipativefashion. In this case, power from the DC power supply 502 can passthrough the diode 510 (or any unidirectional switch) and charge thecapacitor 508 (or any capacitive circuit or device, such as a capacitor)when the switching circuit 504's switching of the plasma load 506appears as a capacitor or an open circuit. Energy stored in thecapacitor 508 can be discharged through the inductor 512 (or anyinductive circuit or device), the switching circuit 504, and to theplasma load 506 without the losses incurred by passing said energythrough a resistor. At the same time, like the resistor 412, theinductor 512 limits the rate of increase in current thus preventing thecapacitor 508 from dangerously discharging its energy during arcingevents.

In an optional embodiment the snubber can include a diode 514 (or anyunidirectional switch) arranged between the inductor and the first rail550 that prevents current from charging the capacitor 508 through theinductor 512. This diode 514 may be required since the inductor 512,rather than the diode 610, is the path of least resistance from thefirst rail 550 to the capacitor 508. The inductor-capacitor (512-508)combination can also lead to ringing, and thus the optional diode 514helps to alleviate this ringing.

However, since the inductor 512 and diode 510 (and optionally the diode514) are arranged in a near-lossless current loop 511, current in theinductor 512 continues to flow with little or no dissipation. Every timean arc occurs, the capacitor 508 discharges some energy in the form ofcurrent through the inductor 512, and then recharges after the arc. Theadded current builds upon the already looping current, and if the rateof arcing is high enough, then the current in the inductor 512 can stepwise build in a runaway current ramp until the current in this loop 511damages or destroys either or both of the diodes 510 and 514.

In some embodiments, a bank of capacitors can replace the capacitor 508such that smaller and less expensive capacitors can be used to achieve alarge capacitance.

FIG. 6 illustrates a power supply system 600 including a DC power supply602, a switching circuit 604, a plasma load 606, and yet anotherembodiment of a non-dissipative snubber circuit. In this case, a switch626 can be arranged between an electrical node 609 (between a diode 610and a capacitor 608) and an inductor 612. The switch 626 can remainclosed during normal processing, but be opened during arc events inorder to cut the near-lossless current loop formed by the inductor 612and the diode 610 (and optionally a diode 614). Thus, whenhigh-frequency arc events occur, a current in the inductor 612 maystepwise rise as a result of each successive discharge from thecapacitor 608. When the current reaches a threshold, the switch 626opens, and the current passes into the capacitor 608 via diode 610 thusproviding a current path for the inductor to discharge through until theenergy stored in the inductor's magnetic field falls and the current inthe inductor 612 drops below the threshold. This prevents the runawaycurrent ramp in the inductor 612 that was described with reference toFIG. 5.

Optionally, the snubber can include a diode 628 (or other unidirectionalswitch) arranged between an electrical node 613 and the second rail 652.The electrical node 613 is arranged between the switch 626 and theinductor 612. The optional diode 628 is forward biased when the switch626 opens, thus providing a current path from the second power rail 652to the inductor 612 and thus enabling the inductor 612 to continue todraw current when the switch 626 opens. This avoids voltage spikesacross the inductor 612. At the same time, the diode 628 is reversebiased when the switch 626 is closed, thus preventing current frompassing to the second power rail 652 after passing through the switch626.

In some embodiments, a bank of capacitors can replace the capacitor 608such that smaller and less expensive capacitors can be used to achieve alarge capacitance.

FIG. 7 illustrates a power supply system 700 including a DC power supply702, a switching circuit 704, a plasma load 706, and yet anotherembodiment of a non-dissipative snubber circuit. Here, a voltagemultiplier 724 replaces the capacitor seen in earlier snubberembodiments. The voltage multiplier 724 is designed to improve theefficiency of the system 700, while still enabling the snubber to absorbpower from the DC power supply 702 and thus protect the switchingcircuit 704.

In particular, and recalling FIGS. 2A and 2B, pulsed DC power systemsoften suffer from slow current ramp rates during each pulse. The voltagemultiplier 724 absorbs power from the DC power supply 702 after theswitching circuit 704 voltage switches, but also boosts process voltage,V₁, to a boosted voltage, V₁+V₂, for a first portion 802 of each pulseso that current ramps faster as illustrated in FIG. 8A. For instance,the DC power supply 702 provides sufficient power to enable the processvoltage V₁, but the voltage multiplier 724 boosts this voltage by V₂during the first portion 802 of each pulse.

This voltage boost is actually a byproduct of the snubber circuitabsorbing power from the DC power supply 702 immediately after 0 Vtransitions of the switching circuit 704. When the switching voltagereaches 0 V, the plasma density drops substantially and the plasma actsmore like an open circuit or an unfluxed inductor than as a lowresistance current path. The DC power supply 702 is current or powerregulated and thus continues to drive the same current level. Thesnubber circuit absorbs this power, which otherwise would be directedinto the switching circuit 704 and potentially damage that circuit.

As current passes into the voltage multiplier 724, energy is storedwithin the voltage multiplier 724 and accumulates along with a voltagethat is increasingly larger than the process voltage V₂ until thecurrent in the plasma has ramped sufficiently to raise the plasmadensity back to a level where power can again be largely provided to theplasma load 706 rather than to the snubber. This time is long enoughthat the voltage across the voltage multiplier 724 builds to greaterthan the process voltage, V₁, and thus for a first portion 802 of eachDC pulse, there is a voltage boost of V₂ as seen in FIG. 8A.

This increased voltage causes the current to ramp faster than seen inthe art (e.g., FIG. 2A). As a result, the current flattens out sooner ineach pulse meaning that greater average power is delivered and thus lesstime is required for a given process. The increased current ramp ratealso means that current does not rise as high as it would given a slowerramp rate, which results in less overall losses (proportional to I²) andless switching losses (proportional to I at the moment of switching).These improvements in efficiency are especially noticeable at higherfrequencies (see FIG. 8B and compare to FIG. 2B).

It should be noted that FIG. 8A is a simplification of the voltage andcurrent waveforms, and in practice the vertical rises and falls may havenon-infinite slopes caused by capacitive and inductive effects.

If the voltage between the first rail 750 and the second rail 752 fallsbelow approximately the process voltage, V₁, then the voltage multiplier724 can partially discharge and supplement the current provided from theDC power supply 702 at approximately the process voltage, V₁.

During arcs, the voltage multiplier 724 can also discharge some of itsenergy through the closed switch 726 and the inductor 712. Anear-lossless current loop 711 may then be established through theinductor 712, the diode 710, and the closed switch 726 (and optionallythe diode 714) until the switch 726 is opened, thus forcing the currentto recharge the voltage multiplier 724.

In some embodiments, V₂=V₁ (e.g., the voltage multiplier 724 is avoltage doubler). However, in other embodiments, V₂ can be less than orgreater than the process voltage, V₁. In some embodiments, V₂ can evenbe variable (see FIGS. 11-14).

In some embodiments, the first diode 710 can be arranged in series witha current limiter such as an inductor (not illustrated) so as to limitnot only the direction of current into the voltage multiplier 724, butto also limit the amount and rate of change of current entering thevoltage multiplier 724. Such a current limiter may be implemented toprevent current overload in the voltage multiplier 724. In embodiments,where two or more of the herein disclosed snubbers are arranged inparallel, the current limiter may limit the current entering each of thesnubbers so that voltage can remain at a reasonable level while stillsending current to each of the two or more snubbers.

In such an embodiment, the current limiter in series with the firstdiode 710 can be selected so that current is able to rapidly enter andcharge the voltage multiplier 724, while the inductor 712 can beselected so that the voltage multiplier 724 discharges at a lowercurrent. This can lead to a rapid boosting of voltage to V₁+V₂ at thestart of each DC pulse (see the first portion 802 of FIGS. 8A and 8B)while the voltage multiplier 724 supplements the DC power supply 702current at V₁ over a longer second portion of each DC pulse.

In one embodiment, the first and second rails 750 and 752 are floating,such that neither is referenced to ground.

The diode 714 can be optional where the LC time constant is long. A“long” LC time constant is one where the inductor 712 current isprevented from reversing direction. In particular, the inductor 712 issinusoidal without the optional diode 714, and so the LC time constantis equal to the switching frequency of the switching circuit 704 andpreferably an order of magnitude greater than the switching frequency ofthe switching circuit 704. The LC time constant can be calculated fromthe inductance of the inductor 712 and any capacitance of the voltagemultiplier 724.

The switching circuit 704 takes either DC voltage or constant power fromthe DC power supply 702 and generates pulsed DC power. Two non-limitingexamples of the switching circuit 704 are an H-bridge (half or fullbridge) or a double-pole double-throw switch network. In an embodiment,the switching circuit 704 can include two or more half or full bridgeH-bridge circuits coupled in series (e.g., one pair of H-bridge outputsfeed the next pair of H-bridge inputs).

The plasma load 706 can be part of a plasma processing chamber, such asthose used in plasma sputtering. Power can be provided to the plasmaload 706 via one or more electrodes such as those in dual-magnetronsputtering (one or more magnetrons can also be used).

FIG. 9 illustrates an embodiment of a power supply system 900 showingdetails of a voltage multiplier 924. The voltage multiplier 924 includesa first capacitor 908 (or a capacitor bank or any capacitive element orsystem), a second capacitor 916, a first diode 918, a second diode 922,and a third diode 920. The first and second capacitors 908 and 916 canbe charged in series when the second diode 922 is forward biased. Thefirst and second capacitors 908 and 916 can then discharge in parallelwhen the first and third diodes 918 and 920 are forward biased, and thesecond diode 922 is reverse biased.

FIG. 10 illustrates an embodiment where the voltage multiplier of thesnubber is a voltage tripler. The voltage multiplier 1024 includes afirst capacitor 1002, a second capacitor 1004, and a third capacitor1006. The voltage multiplier 1024 further includes a first diode 1008, asecond diode 1010, a third diode 1012, a fourth diode 1014, and a fifthdiode 1016. Each of the capacitors 1002, 1004, 1006 can be charged tonear or greater than the process voltage, and therefore when all threeare charged, a voltage drop across all three is around three times theprocess voltage. Thus, the voltage multiplier 1024 is able to boost thevoltage across the first and second rails 1050, 1052 by a factor ofabout three and can therefore be referred to as a voltage tripler.

In some embodiments, a bank of capacitors can replace the capacitors1002, 1004, and 1006 such that smaller and less expensive capacitors canbe used to achieve a large capacitance.

FIG. 11 illustrates a power supply system 1100 including a DC powersupply 1102, a switching circuit 1104, a plasma load 1106, yet anotherembodiment of a snubber circuit 1124, and a voltage multiplier modifier1130. Here, the snubber sees the addition of a voltage multipliermodifier 1130 coupled between a first and second rail 1150, 1152, andhaving an electrical connection to the voltage multiplier 1124. Thevoltage multiplier modifier 1130 can control the effect of the voltagemultiplier 1124 on the voltage, V_(AB), between the rails 1150 and 1152.In this way the boost voltage V₂ (see FIG. 12) can be tailored to adesired amplitude that is less than the maximum boost that the voltagemultiplier 1124 is capable of. Furthermore, the voltage V₂ can be variedin time. This embodiment has particular application where the voltagemultiplier 1124 has a fixed multiplying effect (e.g., a voltage doubleror a voltage tripler).

One application of such control is illustrated in FIG. 12, where avoltage threshold 1202 shows a threshold above which circuitry in thepower supply system 1100 can be damaged. As such the voltage multipliermodifier 1130 can be used to lower V₂ so that the total voltage (V₂+V₁)of the first portion 802 of the pulses remains below the voltagethreshold 1202. As seen, V₂ can be adjusted in time so long as the sumis kept below the voltage threshold 1202.

FIG. 13 illustrates a power supply system showing details of oneembodiment of a voltage multiplier modifier. The voltage multipliermodifier 1330 can include a diode 1334, an inductor 1332, and a switch1336. The combination of the inductor 1332, the switch 1336, and thediode 1334 can function as a discontinuous conduction mode (DCM) boostconverter, where the inductor 1332 current can fall to zero for at leasta portion of operation. The combination can also function as acontinuous conduction mode (CCM) boost converter, where the inductor1332 current never falls to zero.

The inductor 1332 can be arranged between the voltage multiplier 1324and an electrical node 1333, where the electrical node 1333 is arrangedbetween the diode 1334 and the switch 1336. In particular the electricalnode 1333 can be arranged between an anode of the diode 1334 and theswitch 1336. The switch 1336 can be arranged between the electrical node1333 and a second rail 1352. When the switch 1336 closes, stored energyin the voltage multiplier 1324 is removed through the inductivecomponent 1332 and the unidirectional switch 1334 to the first rail1350, thus lowering the voltage across the voltage multiplier 1324 andhence lowering the voltage boost V₂ caused by energy storage in thevoltage multiplier 1324.

The switch 1334 can be turned on and off according to a duty cycle,where a larger duty cycle decreases the voltage boost V₂ from thevoltage multiplier 1324. For instance, a 0% duty cycle (the switch 1334open 100% of the time) allows the full voltage boost V₂ of the voltagemultiplier 1324 to reach the switching circuit 1304.

FIG. 14 illustrates a power supply system showing details of oneembodiment of a voltage multiplier 1424 and of a voltage multipliermodifier 1430. The details of the voltage multiplier modifier 1430 arethe same as those illustrated in FIG. 13, and the details of the voltagemultiplier 1424 are the same as those illustrated in FIG. 9. The voltagemultiplier 1124 can include a first capacitor 1480, a second capacitor1416, a first diode 1418, a second diode 1422, and an optional thirddiode 1420.

During switching of the switching circuit 1404 when the plasma load 1406appears as a capacitor or an open circuit, power from the DC powersupply 1402 passes through the diode 1410 and into the voltagemultiplier 1424. Due to the arrangement of the diodes 1418, 1422, 1420the current charges the first capacitor 1480 and the second capacitor1416 in series while passing through the diodes 1410 and 1422. The diode1418 and the optional diode 1420 are reverse biased during charging ofthe first and second capacitors 1408, 1416.

When the voltage multiplier 1424 discharges, and the voltage multipliermodule 1430 is not active, the second diode 1422 is reverse biased andthe first diode 1418 and the optional third diode 1420, if implemented,are forward biased. As a result, the first and second capacitors 1408and 1416 discharge in parallel. The voltage that the first and secondcapacitors 1408 and 1416 are each charged to can be equivalent to theprocess voltage, V₂, minus a forward bias voltage drop across the diode1410. In other words, the voltage multiplier 1424 approximately doublesthe voltage provided by the DC power supply 1402, and can be referred toas a voltage doubler.

The voltage multiplier modifier 1430 can control how much of the voltagedoubling effect the voltage multiplier 1424 has on V_(AB). For instance,where the switch 1426 has a voltage threshold of 1700 V, and V₁ is 1000V, the voltage multiplier module 1424 by itself would generate a 2000 Vrail voltage on the first rail 1450 and thus damage the switch 1426.However, via proper control of the voltage multiplier modifier 1430 themultiplying effect of the voltage modifier 1424 can be tailored suchthat V^(AB) is kept below 1700 V, thus avoiding damage to the switch1426.

In particular, when the switch 1436 is closed, energy from the capacitor1416 is removed to the second rail 1452 via the inductor 1432 and theclosed switch 1436. As such, the more often the switch 1436 is closed(e.g., a higher duty cycle), the lower the voltage on the capacitor1416. The voltage multiplier modifier 1430 does not affect the voltageon the capacitor 1408. In this fashion, the voltage multiplier modifier1430 can control the boost voltage V₂ provided by the voltage multiplier1424.

When the first and second capacitors 1408, 1416 discharge, and thevoltage multiplier modifier 1430 is active, the first capacitor 1408discharges via the switch 1426, the inductor 1412, and the optionaldiode 1414. Because charge has been removed from the second capacitor1416, the optional diode 1420 is reverse biased, and can be removed fromthe circuit when the voltage multiplier modifier 1430 is used. Thesecond capacitor 1416 discharges through the voltage multiplier modifier1430, and in particular through the inductor 1432 and the diode 1434.

Discussion will now be directed to current paths, voltages, and forwardor reverse biases existing on the various components illustrated in FIG.14 during different phases of operation of one embodiment of a powersupply system. The DC power supply 1402 can be power orcurrent-regulated. During non-arcing conditions, current passes alongfirst rail 1450 from the DC power supply 1402 to the switching circuit1404. The switch 1426 is closed (or on), and the diodes 1410 and 1414are also on, and thus current also passes in a near-lossless loop 1411(see FIG. 17) through the inductor 1412, the diode 1410, the closedswitch 1426, and the diode 1414 (optional). A voltage, V_(AB), is equalto a process voltage during this phase of operation. The process voltageis a voltage across the plasma load 1406 given a steady state plasmaimpedance. This occurs when the plasma is ignited and sustained and thusis conducting, but can vary to some extent depending on plasma stabilityand process conditions (e.g., when reactive gas flow enters the plasmaprocessing chamber). A voltage, V_(EB), as measured from electrical nodeE to electrical node B is equal to the process voltage minus the forwardconduction voltage drop across diode 1410 (e.g., V_(EB)=V_(AB)−V_(AE)).

The constant current loop 1411 maintains the diodes 1410 and 1414(optional) in an on state, thus providing the first rail 1450 instantaccess to the voltage multiplier 1424 should the plasma load impedance1406 rise for any reason. Thus, the voltage multiplier 1424 is ready toabsorb power from the DC power supply 1402 after every 0 V transition ofthe switching circuit 1404 as well as after any malfunction caused by animpedance spike in the plasma load 1406. For instance, where there is aleak in the plasma chamber that suddenly extinguishes the plasma, powerfrom the DC power supply 1402 can be shunted into the voltage multiplier1424.

FIG. 18 illustrates the power supply system of FIG. 14 just after a 0 Vtransition of the switching circuit. After the 0 V transition, theplasma load 1406 impedance rises substantially such that the path ofleast resistance for most of the current is through diode 1410, firstcapacitor 1408, diode 1422, and capacitor 1416 to the second rail 1452.Diode 1418 is reverse biased, as is optional diode 1420 if implemented.The voltage between the rails, V_(AB), when the current begins to takethis route, is equal to the process voltage, V₁. The current charges thecapacitors 1408 and 1416 and in doing so increases V_(AB) above theprocess voltage, V₁. With the illustrated voltage multiplier 1424 (avoltage doubler), V_(AB) can be boosted to substantially twice theprocessing voltage, V₁. In other embodiments, the voltage can be boostedto three, four, or any integer or fractional multiplier of the processvoltage, V₁.

The current running along this path and the corresponding charging ofthe first and second capacitors 1408 and 1416 gradually falls off as thecapacitors 1408 and 1416 are charged. Eventually the current flow tapersto a negligible amount or the current in the plasma ramps sufficientlyto draw down the plasma load 1406 impedance to normal levels, such thatpower again is delivered to the plasma load 1406. When this happens, thevoltage across the voltage multiplier, V_(EB), is typically large enoughto forward bias diode 1418 as well as optional diode 1420 ifimplemented, and diode 1422 turns off. The resulting current flow anddiode biasing is illustrated in FIG. 19. Here, the capacitors 1408 and1416 discharge in parallel through the closed switch 1426, the inductor1412, and the optional diode 1414 until the capacitors 1408 and 1416return to a voltage at which diodes 1418 and 1420 turn off (e.g., nearprocess voltage).

In embodiments, where the voltage multiplier modifier 1430 is used toremove some portion of charge on the second capacitor 1416, optionaldiode 1420 is not needed, and in such embodiments the optional diode1420 is reverse biased even if implemented. Either way, the secondcapacitor 1416 discharges via the inductor 1432 and diode 1434 ratherthan via the illustrated current path through optional diode 1420.

As the capacitors 1408 and 1416 discharge, the voltage V_(AB) drops fromV₁+V₂ to V₁ or the process voltage as seen in FIGS. 8A and 8B. However,this current flow can also cause the voltage fall time to be finite asillustrated in FIGS. 25A and 25B. FIGS. 25A and 25B illustrate the plotsin FIGS. 8A and 8B, but include detail of the sloped voltage decrease2500 attributable to the discharge of the capacitors 1408 and 1416 afterthe plasma impedance falls to normal levels.

As seen, diode 1410 is still forward biased, thus continuing to providean instant shunt for power from the DC power supply 1402 to the voltagemultiplier 1424 should it be needed. Even small amounts of power fromthe DC power supply 1402 can be directed into the voltage multiplier1424, where the energy builds until the diodes 1418 and 1420 turn on andbegin to discharge the capacitors 1408 and 1416. In this way, thecapacitors 1408 and 1416 remain at voltages near or slightly aboveprocess voltage.

FIG. 20 illustrates the current paths and diode biases in the powersupply system of FIG. 14 during a single arc event. During an arc, theplasma load impedance 1406 drops causing the voltage V_(AB) to drop.When this happens, the voltage V_(AB) typically falls below the voltageV_(EB), which reverse biases the diode 1410 (illustrated as forwardbiased). While the voltage multiplier 1424 does discharge energy intothe arc, the discharge is not large since the inductor 1412 limits therise in current. In some cases, the inductor 1412 can be selected to beso large, that even during such an arc, the current does not appreciablyrise. Thus, the voltage multiplier 1424 does not threaten to exacerbatearcs.

The current leaves the snubber and heads to the switching circuit 1404as well as back into the near-lossless loop 1411. If two arcs occurback-to-back, then the current in the inductor 1412 may step upwards dueto multiple discharges from the capacitors in the voltage multiplier1424. A series of arcs in rapid succession can stepwise increase thecurrent to levels that could damage the diodes 1410 and 1414. Thus, whenthe current in the inductor 1412 reaches a threshold, the switch 1426opens as seen in FIG. 21. The opening of the switch 1426 cuts thenear-lossless loop 1411 and forces the inductor 1412 current todischarge into the voltage multiplier 1424. The inductor 1412 currentramps down and thus opening of the switch 1426 avoids runaway stepwisecurrent ramping in the near-lossless loop 1411.

The current is illustrated as leaving the optional diode 1414 andheading either back to the diode 1410 or to the switching circuit 1404.In some cases, both current paths will be used. However, where theswitching circuit 1404 is open, current does not pass to the switchingcircuit 1404 and instead all current passes through diode 1410 to thevoltage multiplier 1424. In cases where the switching circuit 1404 isclosed and there is an arc, current will prefer the path into theswitching circuit 1404 and the arc. However, after the arc has ceased,or at least diminished, current may be more equally split between thetwo paths.

Optional diode 1428 can be included between the inductor 1412 and thesecond rail 1452 to provide a current path to the inductor 1412 when theswitch 1426 opens, thereby avoiding voltage spikes in the inductor 1412.

In an alternative embodiment, where a boost voltage V₂ equal to theprocess voltage V₁ is desired, the voltage multiplier modifier 1430 canbe used for overvoltage protection via a hysteresis control algorithm.Although the voltage multiplier 1424 typically generates a boostedvoltage V₁+V₂ during a first portion of each pulse, in some instancesthere may be transient voltages that threaten the circuitry or thesubstrate processing. To mitigate such transients, the switch 1436 canclose when a voltage across the second capacitor 1416 rises above amaximum voltage threshold V_(max). In an alternative, the switch 1436can begin switching at a defined duty cycle configured to lower avoltage across the second capacitor 1416. Alternatively, the switch 1436may already be switching when the voltage across the second capacitor1416 rises above the maximum voltage threshold V_(max). In this case theswitch 1436 can increase its duty cycle so as to lower the voltageacross the second capacitor 1416.

Whichever of these methods is implemented, the switch 1436 persists inoperation (e.g., closed, defined duty cycle, or an increased duty cycle)until the voltage across the second capacitor 1416 falls below a minimumvoltage threshold V_(min). The switch 1436 can then open or decrease itsduty cycle. The switch 1436 can remain open or maintain the decreasedduty cycle until the voltage again exceeds the maximum voltage thresholdV_(max). This overvoltage hysteresis control prevents transient voltagesfrom damaging the electronics or generating unwanted high energy ions inthe plasma.

The value V_(max)−V_(min) defines the duty cycle of the switch 1436 as amultiple of the double of the switch 1436, because the first and secondcapacitors 1408, 1416 are only charged during a first portion of eachpulse from the switching circuit 1404, when the plasma has a highimpedance and thus cannot draw the full current delivered from the DCpower supply 1402, the inductor 1412, and the inductor 1432.

A voltage sensor (not illustrated) can monitor a voltage across thesecond capacitor 1416 and provide feedback to a control of the switch1436 to control opening and closing of the switch 1436 or a duty cycleof the switch 1436. In other words, the switch 1436 can open and close,or have a duty cycle, responsive to feedback from a voltage sensormonitoring the voltage across the second capacitor 1416.

FIG. 15 illustrates a power supply system including a DC power supplyproviding power to a switching circuit, which then provides pulsed DCpower to a plasma load. A snubber 1508 can be incorporated into the DCpower supply 1502, and power can be provided from the snubber 1508 tothe switching circuit 1504.

FIG. 16 illustrates a power supply system including a DC power supplyproviding power to a switching circuit, which then provides pulsed DCpower to a plasma load. A snubber 1608 can be incorporated into theswitching circuit 1604, and power can be provided from the DC powersupply 1602 to the snubber 1608.

FIG. 26 illustrates a method of controlling power in a power supplysystem. The method 2600 can begin with the passage of power from a powersupply (e.g., DC power supply) to a load via a pass power operation2602. The load can have an impedance, and the impedance can change intime. When the impedance substantially increases, an absorbing at leastsome of the power operation 2604 can absorb at least some of the powerfrom the power supply. Absorption of the power can cause a boost orincrease to voltage and current reaching the load (e.g., 8A, 8B, 12,25). After absorption of the power, the method 2600 can include adischarging at least some of the absorbed power operation 2606 where atleast some of the absorbed power is discharged into the load. Thisdischarge can be activated by a decrease in the load impedance and cantake place in a substantially non-dissipative fashion. After thedischarge operation 2606, the method 2600 can end or return to thepassing power operation 2602.

Although this disclosure has focused on embodiments where snubbers areused to mitigate voltage and current spikes (or ramps) in a power supplysystem, and in particular for pulsed DC applications, it is envisionedthat the disclosed snubber can be used in a variety of other voltageand/or current clamping situations.

FIG. 22 illustrates another embodiment of a power supply system. A powersupply (DC or AC) 2002 provides power to a load 2006 via first andsecond rails 2050 and 2052. The load 2006 can be a plasma load or anyother type of load (e.g., a DC or AC electrical motor). A singlemagnetron sputtering system is one implementation of such a power supplysystem. A snubber 2004 can be coupled to the rails 2050 and 2052 betweenthe power supply 2002 and the load 2006 and can be configured to absorbpower from the power supply 2002 when an impedance of the load 2006increases. As the load 2006 impedance decreases, the snubber 2004 candischarge some of its stored energy into the load 2006 to supplementpower from the power supply 2002. Because little to no energy isdissipated in the snubber 2004, the snubber can be referred to as anon-dissipative snubber.

The snubber 2004 is further configured to temporarily boost a voltage asmeasured from the first rail 2150 to the second rail 2152, again in anon-dissipative manner. If the power supply 2002 is a power-regulatedsupply, then the voltage boost will result in faster current rampingwhen the power is first applied, or when power is reapplied in a pulsingcontext. This can decrease power turn on time, which can be useful insemiconductor fabrication applications, to name one example. Forinstance, where there is a problem with the load 2006 that drives theload 2006 impedance high (e.g., loss of plasma conductivity in a plasmaprocessing chamber), power can be more quickly reapplied to the load2006 after the problem has been resolved than with known snubbers.

FIG. 23 illustrates yet another power supply system. A power supply (DCor AC) 2102 provides power to a load 2106 via first and second rails2150 and 2152 and via vulnerable circuitry 2106. Vulnerable circuitryincludes any circuitry that can be damaged by excessive currents orpower and in particular can be damaged when an impedance of the load2108 increases. A snubber 2104 can be coupled to the rails 2150 and 2152between the power supply 2102 and the vulnerable circuitry 2106 and canbe configured to absorb power from the power supply 2102 when animpedance of the load 2108 increases. In this way the snubber 2104 canprevent excessive power or currents from passing through the vulnerablecircuitry 2106 and damaging components therein.

Returning to FIG. 24 illustrates yet a further power supply system. Thepower supply system 2400 can include a power supply 2402, a load 2406, anon-dissipative snubber 2460, and optionally vulnerable circuitry 2404.The snubber 2460 can be arranged between the power supply 2402 and theload 2406. The optional vulnerable circuitry 2404 can be arrangedbetween the snubber 2460 and the load 2406.

The snubber 2460 functions much like the snubbers disclosed throughoutthis disclosure. However, the snubber 2460 does so using moregeneralized components, in order to show applications outside of thepulsed DC environment. For instance, rather than diodes, the snubber2460 can include unidirectional switches 2410, 2414, and 2416. Thesnubber 2460 can also include an optional current limiter 2408 in serieswith the unidirectional switch 2410 as well as a current limiter 2412 inseries with the unidirectional switch 2414. The snubber 2460 includes aswitch 2422 and a voltage multiplier 2418. Optionally, the snubber 2460can include a voltage multiplier modifier 2420. The snubber 2460 mayfurther include an optional unidirectional switch 2404 arranged betweenthe current limiter 2412 and the second rail 2452.

In some embodiments, the unidirectional switch 2410 can be arranged inseries with the optional current limiter 2408, such as an inductor, soas to limit not only the direction of current into the voltagemultiplier 2424, but to also limit the amount and rate of change ofcurrent entering the voltage multiplier 2424. Such an optional currentlimiter 2408 may be implemented to prevent current overload in thevoltage multiplier 2424. In embodiments, where two or more of the hereindisclosed snubbers 2460 are arranged in parallel, the optional currentlimiter 2408 may limit the current entering each of the snubbers so thatvoltage can remain at a reasonable level while still sending current toeach of the two or more snubbers.

In such an embodiment, the optional current limiter 2408 in series withthe first unidirectional switch 2410 can be selected so that current isable to rapidly enter and charge the voltage multiplier 2418, while thecurrent limiter 2412 can be selected so that the voltage multiplier 2418discharges at a lower current. This can lead to a rapid boosting ofvoltage to V₁+V₂ at the start of each DC pulse (see the first portion802 of FIGS. 8A and 8B) while the voltage multiplier 2418 supplementsthe power supply 2402 current at V₁ over a longer second portion of eachDC pulse.

In one embodiment, the first and second rails 2450 and 2452 arefloating, such that neither is referenced to ground. The optionalunidirectional switch 2414 can be excluded where an LC time constant islong. A “long” LC time constant is long enough to prevent the currentlimiter 2412 current from reversing direction. In particular, current inthe current limiter 2412 would be sinusoidal without the optionalunidirectional switch 2414, and so the LC time constant is preferablyequal to a switching frequency of the vulnerable circuitry 2404,assuming the vulnerable circuitry 2404 includes a switching frequency.In a further preferred embodiment, the LC time constant is an order ofmagnitude greater than the switching frequency of the vulnerablecircuitry 2404, assuming the vulnerable circuitry 2404 includes aswitching frequency. The LC time constant can be calculated from theinductance of the current limiter 2412 and any capacitance of thevoltage multiplier 2424. Two non-limiting examples of the vulnerablecircuitry 2404 are an H-bridge (half or full bridge) and a double-poledouble-throw switch network.

The load 2406 can be part of a plasma processing chamber, such as thoseused in plasma sputtering. Power can be provided to the load 2406 viaone or more electrodes such as those in dual-magnetron sputtering (oneor more magnetrons can also be used).

The systems and methods described herein can be implemented in a machinesuch as a computer system in addition to the specific physical devicesdescribed herein. FIG. 27 shows a diagrammatic representation of oneembodiment of a machine in the exemplary form of a computer system 2700within which a set of instructions can execute for causing a device toperform or execute any one or more of the aspects and/or methodologiesof the present disclosure. The components in FIG. 27 are examples onlyand do not limit the scope of use or functionality of any hardware,software, embedded logic component, or a combination of two or more suchcomponents implementing particular embodiments.

Computer system 2700 may include a processor 2701, a memory 2703, and astorage 2708 that communicate with each other, and with othercomponents, via a bus 2740. The bus 2740 may also link a display 2732,one or more input devices 2733 (which may, for example, include akeypad, a keyboard, a mouse, a stylus, etc.), one or more output devices2734, one or more storage devices 2735, and various tangible storagemedia 2736. All of these elements may interface directly or via one ormore interfaces or adaptors to the bus 2740. For instance, the varioustangible storage media 2736 can interface with the bus 2740 via storagemedium interface 2726. Computer system 2700 may have any suitablephysical form, including but not limited to one or more integratedcircuits (ICs), printed circuit boards (PCBs), mobile handheld devices(such as mobile telephones or PDAs), laptop or notebook computers,distributed computer systems, computing grids, or servers.

Processor(s) 2701 (or central processing unit(s) (CPU(s))) optionallycontains a cache memory unit 2702 for temporary local storage ofinstructions, data, or computer addresses. Processor(s) 2701 areconfigured to assist in execution of computer readable instructions.Computer system 2700 may provide functionality as a result of theprocessor(s) 2701 executing software embodied in one or more tangiblecomputer-readable storage media, such as memory 2703, storage 2708,storage devices 2735, and/or storage medium 2736. The computer-readablemedia may store software that implements particular embodiments, andprocessor(s) 2701 may execute the software. Memory 2703 may read thesoftware from one or more other computer-readable media (such as massstorage device(s) 2735, 2736) or from one or more other sources througha suitable interface, such as network interface 2720. The software maycause processor(s) 2701 to carry out one or more processes or one ormore steps of one or more processes described or illustrated herein.Carrying out such processes or steps may include defining datastructures stored in memory 2703 and modifying the data structures asdirected by the software.

The memory 2703 may include various components (e.g., machine readablemedia) including, but not limited to, a random access memory component(e.g., RAM 2704) (e.g., a static RAM “SRAM”, a dynamic RAM “DRAM, etc.),a read-only component (e.g., ROM 2705), and any combinations thereof.ROM 2705 may act to communicate data and instructions unidirectionallyto processor(s) 2701, and RAM 2704 may act to communicate data andinstructions bidirectionally with processor(s) 2701. ROM 2705 and RAM2704 may include any suitable tangible computer-readable media describedbelow. In one example, a basic input/output system 2706 (BIOS),including basic routines that help to transfer information betweenelements within computer system 2700, such as during start-up, may bestored in the memory 2703.

Fixed storage 2708 is connected bidirectionally to processor(s) 2701,optionally through storage control unit 2707. Fixed storage 2708provides additional data storage capacity and may also include anysuitable tangible computer-readable media described herein. Storage 2708may be used to store operating system 2709, EXECs 2710 (executables),data 2711, API applications 2712 (application programs), and the like.Often, although not always, storage 2708 is a secondary storage medium(such as a hard disk) that is slower than primary storage (e.g., memory2703). Storage 2708 can also include an optical disk drive, asolid-state memory device (e.g., flash-based systems), or a combinationof any of the above. Information in storage 2708 may, in appropriatecases, be incorporated as virtual memory in memory 2703.

In one example, storage device(s) 2735 may be removably interfaced withcomputer system 2700 (e.g., via an external port connector (not shown))via a storage device interface 2725. Particularly, storage device(s)2735 and an associated machine-readable medium may provide nonvolatileand/or volatile storage of machine-readable instructions, datastructures, program modules, and/or other data for the computer system2700. In one example, software may reside, completely or partially,within a machine-readable medium on storage device(s) 2735. In anotherexample, software may reside, completely or partially, withinprocessor(s) 2701.

Bus 2740 connects a wide variety of subsystems. Herein, reference to abus may encompass one or more digital signal lines serving a commonfunction, where appropriate. Bus 2740 may be any of several types of busstructures including, but not limited to, a memory bus, a memorycontroller, a peripheral bus, a local bus, and any combinations thereof,using any of a variety of bus architectures. As an example and not byway of limitation, such architectures include an Industry StandardArchitecture (ISA) bus, an Enhanced ISA (EISA) bus, a Micro ChannelArchitecture (MCA) bus, a Video Electronics Standards Association localbus (VLB), a Peripheral Component Interconnect (PCI) bus, a PCI-Express(PCI-X) bus, an Accelerated Graphics Port (AGP) bus, HyperTransport(HTX) bus, serial advanced technology attachment (SATA) bus, and anycombinations thereof.

Computer system 2700 may also include an input device 2733. In oneexample, a user of computer system 2700 may enter commands and/or otherinformation into computer system 2700 via input device(s) 2733. Examplesof an input device(s) 2733 include, but are not limited to, analpha-numeric input device (e.g., a keyboard), a pointing device (e.g.,a mouse or touchpad), a touchpad, a joystick, a gamepad, an audio inputdevice (e.g., a microphone, a voice response system, etc.), an opticalscanner, a video or still image capture device (e.g., a camera), and anycombinations thereof. Input device(s) 2733 may be interfaced to bus 2740via any of a variety of input interfaces 2723 (e.g., input interface2723) including, but not limited to, serial, parallel, game port, USB,FIREWIRE, THUNDERBOLT, or any combination of the above.

In particular embodiments, when computer system 2700 is connected tonetwork 2730, computer system 2700 may communicate with other devices,specifically mobile devices and enterprise systems, connected to network2730. Communications to and from computer system 2700 may be sentthrough network interface 2720. For example, network interface 2720 mayreceive incoming communications (such as requests or responses fromother devices) in the form of one or more packets (such as InternetProtocol (IP) packets) from network 2730, and computer system 2700 maystore the incoming communications in memory 2703 for processing.Computer system 2700 may similarly store outgoing communications (suchas requests or responses to other devices) in the form of one or morepackets in memory 2703 and communicated to network 2730 from networkinterface 2720. Processor(s) 2701 may access these communication packetsstored in memory 2703 for processing.

Examples of the network interface 2720 include, but are not limited to,a network interface card, a modem, and any combination thereof. Examplesof a network 2730 or network segment 2730 include, but are not limitedto, a wide area network (WAN) (e.g., the Internet, an enterprisenetwork), a local area network (LAN) (e.g., a network associated with anoffice, a building, a campus or other relatively small geographicspace), a telephone network, a direct connection between two computingdevices, and any combinations thereof. A network, such as network 2730,may employ a wired and/or a wireless mode of communication. In general,any network topology may be used.

Information and data can be displayed through a display 2732. Examplesof a display 2732 include, but are not limited to, a liquid crystaldisplay (LCD), an organic liquid crystal display (OLED), a cathode raytube (CRT), a plasma display, and any combinations thereof. The display2732 can interface to the processor(s) 2701, memory 2703, and fixedstorage 2708, as well as other devices, such as input device(s) 2733,via the bus 2740. The display 2732 is linked to the bus 2740 via a videointerface 2722, and transport of data between the display 2732 and thebus 2740 can be controlled via the graphics control 2721.

In addition to a display 2732, computer system 2700 may include one ormore other peripheral output devices 2734 including, but not limited to,an audio speaker, a printer, and any combinations thereof. Suchperipheral output devices may be connected to the bus 2740 via an outputinterface 2724. Examples of an output interface 2724 include, but arenot limited to, a serial port, a parallel connection, a USB port, aFIREWIRE port, a THUNDERBOLT port, and any combinations thereof.

In addition or as an alternative, computer system 2700 may providefunctionality as a result of logic hardwired or otherwise embodied in acircuit, which may operate in place of or together with software toexecute one or more processes or one or more steps of one or moreprocesses described or illustrated herein. Reference to software in thisdisclosure may encompass logic, and reference to logic may encompasssoftware. Moreover, reference to a computer-readable medium mayencompass a circuit (such as an IC) storing software for execution, acircuit embodying logic for execution, or both, where appropriate. Thepresent disclosure encompasses any suitable combination of hardware,software, or both.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such the processorcan read information from, and write information to, the storage medium.In the alternative, the storage medium may be integral to the processor.The processor and the storage medium may reside in an ASIC. The ASIC mayreside in a user terminal. In the alternative, the processor and thestorage medium may reside as discrete components in a user terminal.

One of skill in the art will recognize that the plots of voltage andcurrent (e.g., FIGS. 2A, 2B, 8A, 8B, 25A, and 25B are not necessarilydrawn to scale, and that the shape and scale of different features ofthe waveforms can change depending on the circuits used to generatethese waveforms. For instance, the pulse width of the voltage increaseat the start of each pulse may vary depending on the power passing tothe snubber and depending on capacitance values within the snubber(e.g., the capacitances of the first capacitor 1408 and the secondcapacitor 1416 in FIG. 14). As another example, vertical aspects of thevoltage pulses illustrated in FIGS. 8A and 8B may have less thaninfinite slope in practice. For instance, the falling edge of theboosted voltage (the first portion of each pulse) can have a negativeslope that is a function of inductance and capacitance. The frontvertical aspect of each pulse can in practice include an exponentiallyincreasing portion for V₂ where the boost voltage rises above V₁ as afunction of charge accumulation on the capacitors 1408 and 1416 in FIG.14. Furthermore, while the current waveforms show a flat or near flatportion during a latter portion of each pulse, in practice the slope ofthis portion of the current waveform can vary and be non-zero. Theseexamples demonstrate that the plots of voltage and current in thefigures are meant as illustrations and generalizations only, and thatvariations on these specific waveforms can be made without departingfrom the scope of this disclosure.

FIG. 28 illustrates an alternative topology for a voltage-boostingcircuit of a pulsed DC power supply system. The voltage-boosting circuit2804 can have functionality of a snubber and can be used to both boostthe rail voltage V_(AB) as well as to absorb current and/or power from aDC power supply providing power to the rails 2850, 2852. Thevoltage-boosting circuit 2804 includes a first diode 2810, a capacitor2812, a switch 2814, a second diode 2816, a third diode 2818, and aninductor 2820. Unlike other voltage-boosting circuits having snubberfunctionality, here the switch 2814 remains open (off) until thecapacitor 2812 charges to a desired boosted voltage (V₁+V₂). Othervoltage-boosting circuits can be limited to a boosted voltage equal totwice the process voltage (V₁) and greater than twice the average railvoltage V_(AB). Because the switch 2814 of the illustratedvoltage-boosting circuited 2804 can be left open indefinitely, thecapacitor 2812 can charge to greater than twice the process voltage (V₁)and greater than twice the average rail voltage V_(AB). Charge andvoltage on the capacitor 2812 is in part a function of a duty cycle ofthe switch 2814.

When the switching circuit 2806 switches and plasma impedance rises, sodoes the rail voltage V_(AB). This rise in rail voltage V_(AB) forwardbiased the first diode 2810 allowing current to run into the capacitor2812 and charge the voltage across the capacitor 2812. When the switch2814 is open (off) the capacitor 2812 can be charged as long as the railvoltage V_(AB) is greater than the capacitor 2812 voltage plus a diodevoltage drop across the first diode 2810. The capacitor 2812 voltage cantherefore be charged to voltages greater than twice a process voltage V₁and twice an average rail voltage V_(AB).

When the switch is closed (on) the capacitor 2812 discharges throughinductor 2820 raising the instantaneous rail voltage V_(AB). As thecapacitor 2812 discharges, the instantaneous rail voltage V_(AB)decreases until the instantaneous rail voltage V_(AB) is lower than avoltage across the capacitor 2812, at which point the first diode 2810becomes reverse biased and current ceases to charge the capacitor 2812.The rail voltage V_(AB) then remains at this voltage, a process voltageV₁, until switching occurs and the plasma impedance again rises andforward biases the first diode 2810. When the switch 2814 opens, thethird diode 2818 provides a current path to the inductor 2820 to enablecurrent to continue flowing through the inductor 2820 as the currentramps down.

One of skill in the art will recognize that the voltage-boosting circuit2805 can be implemented for the snubbers described with reference toFIGS. 1-27.

FIG. 29 illustrates another embodiment of a voltage-boosting circuit2904 having snubber functionality. The voltage-boosting circuit 2905includes a first diode 2910, a first switch 2926, a second and optionalswitch 2936, a first inductor 2912, a second inductor 2932, a seconddiode 2930, a third and optional diode 2928, and a voltage multiplier2924. The voltage multiplier 2924 includes a first capacitor 2908, asecond capacitor 2916, a fourth diode 2918, and a fifth diode 2922.

The optional second switch 2936 is typically open, or in its absence,the second inductor 2932 is merely coupled to a first rail 2950 via thesecond diode 2930. The first switch 2926 typically is closed (on).

When the switching circuit 2904 switches, the plasma impedance rises asdoes the rail voltage V_(AB), which forward biases the first diode 2910and sends current into the voltage multiplier 2924. In particular, thecurrent charges the first capacitor 2908 and charges the secondcapacitor 2916. Both capacitors 2908, 2916 charge until an average railvoltage V_(AB) is seen across each capacitor 2908, 2916.

Although the capacitors 2908, 2916 each charge to the average railvoltage V_(AB), they can see instantaneous voltage in excess of theaverage rail voltage V_(AB), and for safety, there is a desire tomitigate these overvoltages. This is where the optional second switch2936 can be used. The optional second switch 2936 can operate accordingto a hysteresis control algorithm. The optional second switch 2936 canclose when a voltage across the second capacitor 2916 rises above amaximum voltage threshold V_(max). In an alternative, the secondoptional switch 2936 can begin switching at a defined duty cycleconfigured to lower a voltage across the second capacitor 2916.Alternatively, the second optional switch 2936 may already be switchingwhen the voltage across the second capacitor 2916 rises above themaximum voltage threshold V_(max). In this case the second optionalswitch 2936 can increase its duty cycle so as to lower the voltageacross the second capacitor 2916.

Whichever of these methods is implemented, the second optional switch2936 persists in operation (e.g., closed, defined duty cycle, or anincreased duty cycle) until the voltage across the second capacitor 2916falls below a minimum voltage threshold V_(min). The second optionalswitch 2936 can then open or decrease its duty cycle. The secondoptional switch 2936 can remain open or maintain the decreased dutycycle until the voltage again exceeds the maximum voltage thresholdV_(max). This overvoltage hysteresis control prevents transient voltagesfrom damaging the electronics or generating unwanted high energy ions inthe plasma.

The value V_(max)−V_(min) defines the duty cycle of the second optionalswitch 2936 as a multiple of the double of the second optional switch2936, because the first and second capacitors 2908, 2916 are onlycharged during a first portion of each pulse from the switching circuit2904, when the plasma has a high impedance and thus cannot draw the fullcurrent delivered from the DC power supply 2902, the first inductor2912, and the second inductor 2932.

A voltage sensor (not illustrated) can monitor a voltage across thesecond capacitor 2916 and provide feedback to a control of the optionalsecond switch 2936 to control opening and closing of the optional secondswitch 2936 or a duty cycle of the optional second switch 2936. In otherwords, the optional second switch 2936 can open and close, or have aduty cycle, responsive to feedback from a voltage sensor monitoring thevoltage across the second capacitor 2916.

As noted earlier, while this discussion has focused on embodiments wherea single pulsed DC power supply system powers a single anodelesselectrode pair, in other embodiments, multiple anodeless electrode pairscan be implemented. In some cases, a single pulsed DC power supplysystem can provide pulsed DC power to each anodeless electrode pair,while in other embodiments, there may be a separate pulsed DC powersupply system for each anodeless electrode pair.

In one embodiment, the use of a plurality of pulsed DC power supplysystems each feeding one of a plurality of anodeless electrode pairs,can be paired with different boost voltages V₂ to each electrode pair soas to effectuate a desired processing effect including a desired filmproperty (e.g., optical characteristic, resistance, and stress) orprocessing characteristic (e.g., sputtering rate).

For instance, an embodiment could include a first pulsed DC power supplysystem providing a first pulsed DC power to a first anodeless electrodepair, the first pulsed DC power having a first boost voltage V2, and asecond pulsed DC power supply system providing a second pulsed DC powerto a second sputtering cathode and a second anode, the second pulsed DCpower having a second boost voltage V2′. In another embodiment, thefirst boost voltage V2 can be provided to a first anodeless electrodewhile the second boost voltage V2′ can be provided to a second anodelesselectrode. The first and second anodeless electrodes can both operate asan anode, a cathode, and a sputtering target and may be adjacent to eachother (e.g., no targets or electrodes separate the first and secondanodeless electrode). V2 and V2′ can be non-equal and thus effectuate adesired processing effect. In this way, not only can different processvoltages, different duty cycles, and different frequencies be applied todifferent electrodes, but additional control over the boost voltages todifferent anodeless electrode pairs is now possible.

FIG. 30 illustrates an embodiment of a power supply system including twoor more pulsed DC power supply systems providing pulsed DC power to fouror more anodeless electrodes in a plasma processing chamber. Each pulsedDC power supply 3001, 3002 can embody any of the circuits andfunctionality as described earlier with reference to various embodimentsof pulsed DC power supply systems (e.g., FIGS. 1-28). The pulsed DCpower supply systems 3001, 3002 can generate pulsed DC power having aboosted voltage (V₁+V₂) during a first portion of each pulse (e.g., FIG.12).

Each pulsed DC power supply system 3001, 3002 can power a pair ofanodeless electrodes. For instance, the first pulsed DC power supplysystem 3001 provides pulsed DC voltage having a voltage V_(CD) to firstand second anodeless electrodes 3010, 3012. The second pulsed DC powersupply system 3002 provides pulsed DC voltage having a voltage V_(EF) tothird and fourth anodeless electrodes 3014, 3016. The anodelesselectrodes operate as anodes, cathodes, and sputtering targets.

The boost voltage V₂ provided by each pulsed DC power supply system3001, 3002 can be selectable and differ from one pulsed DC power supplyto another. For instance, a first boost voltage V₂ can be applied to thefirst and second anodeless electrodes 3010, 3012, while a second boostvoltage V_(2′) can be applied to the third and fourth anodelesselectrodes 3014, 3016.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A pulsed DC power supply system providing pulsedDC power to a plurality of anodeless electrodes sustaining a plasma in aplasma processing chamber, the pulsed DC power supply system comprising:a first DC power supply supplying a first DC power to a first and asecond rail having a first rail voltage therebetween; a first switchingcircuit receiving the first DC power via the first and second rails andconverting the first DC power to a first pulsed DC voltage configuredfor delivery to at least a first anodeless electrode of the plasmaprocessing chamber; a first voltage-boosting circuit coupled between thefirst and second rails, the first voltage-boosting circuit including afirst voltage multiplier and a first voltage multiplier modifier, thefirst voltage multiplier configured to draw current from the first DCpower supply when an impedance of a plasma load increases therebyraising the first rail voltage by a first boost voltage V₂, the firstboost voltage V₂ being selectable by the first voltage multipliermodifier; a second DC power supply supplying a second DC power to athird and fourth rail having a second rail voltage therebetween; asecond switching circuit receiving the second DC power via the third andfourth rails and converting the second DC power to a second pulsed DCvoltage configured for delivery to at least a second anodeless electrodeof the plasma processing chamber; and a second voltage-boosting circuitcoupled between the first and second rails, the second voltage-boostingcircuit including a second voltage multiplier and a second voltagemultiplier modifier, the second voltage multiplier configured to drawcurrent from the second DC power supply when the impedance of the plasmaload increases thereby raising the second rail voltage by a second boostvoltage V_(2′), the second boost voltage V_(2′) being selectable by thesecond voltage multiplier modifier.
 2. The pulsed DC power supply systemof claim 1, wherein the first voltage-boosting circuit includes one ormore capacitive elements configured to absorb the current from the firstDC power supply when the impedance of the plasma load increases.
 3. Thepulsed DC power supply system of claim 1, wherein the one or morecapacitive elements of the first voltage-boosting circuit are arrangedto absorb the current in series and to discharge current back to thefirst rail in parallel.
 4. The pulsed DC power supply system of claim 3,wherein a first of the two capacitive elements charges to the processvoltage V₁ during a first portion of each pulse, while the secondcapacitive element charges to the first boost voltage V₂ during thefirst portion of each pulse.
 5. The pulsed DC power supply system ofclaim 4, wherein the first voltage-boosting circuit includes a switchhaving a duty cycle that controls a magnitude of the first boost voltageV₂.
 6. The pulsed DC power supply system of claim 1, wherein the firstvoltage multiplier modifier controls a magnitude of the first boostvoltage V₂.
 7. A pulsed DC power supply system configured to providepulsed DC power to a plurality of anodeless electrodes of a plasmaprocessing chamber, the pulsed DC power supply comprising: a firstpulsed DC power supply system providing a DC current via a first andsecond rail; a first voltage-boosting circuit coupled between the firstand second rail and periodically boosting a voltage of the rail by afirst selectable boost voltage; a first switching circuit receiving theDC current via the first and second rail and generating a first pulsedDC voltage that is periodically boosted above a process voltage by thefirst selectable boost voltage; and first and second outputs configuredto provide the first pulsed DC voltage to first and second anodelesselectrodes, the first selectable boost voltage being different than asecond selectable boost voltage configured to be provided to third andfourth anodeless electrodes.
 8. The pulsed DC power supply system ofclaim 7, wherein the second selectable boost voltage is powered from DCcurrent from a second pulsed DC power supply system.
 9. The pulsed DCpower supply system of claim 8, further comprising a third outputconfigured to provide pulsed DC power to a third anodeless electrode.10. The pulsed DC power supply system of claim 9, wherein the secondpulsed DC power supply system is coupled to the third output.
 11. Thepulsed DC power supply system of claim 9, wherein the first pulsed DCpower supply system is coupled to the third output.
 12. The pulsed DCpower supply system of claim 7, wherein the first voltage-boostingcircuit includes: a capacitive element between the first and secondrail; a current-limiting element coupling the capacitive element to thefirst rail; and a switch controlling a current between the capacitiveelement and the current-limiting element, the switch having a duty cyclethat controls the current and controls the boost voltage V₂.
 13. Thepulsed DC power supply system of claim 12, wherein the current-limitingelement is an inductive element.
 14. The pulsed DC power supply systemof claim 13, wherein the inductive element is an inductor.
 15. A methodcomprising: delivering a first bipolar pulsed DC voltage to a firstanodeless electrode in a plasma processing chamber; delivering a secondpulsed DC voltage to a second anodeless electrode in the plasmaprocessing chamber, the first pulsed DC voltage having a boosted voltageV₁+V₂ magnitude for a first portion of each pulse of the first pulsed DCvoltage, the second pulsed DC voltage having a boosted voltage V₁+V_(2′)magnitude for a first portion of each pulse of the second pulsed DCvoltage, each DC pulse in the first and second pulsed DC voltages havingan opposite polarity to a previous pulse.
 16. The method of claim 15,wherein control of a process voltage V₁ is independent of control over afirst boost voltage V₂ and a second boost voltage V_(2′), and whereincontrol over the first boost voltage V₂ is independent of control overthe second boost voltage V_(2′).
 17. The method of claim 15, wherein thefirst and second anodeless electrodes are adjacent to each other. 18.The method of claim 15, wherein the first and second anodelesselectrodes are spaced from each other by at least one other anodelesselectrode.
 19. A pulsed DC power supply system comprising: two or morepulsed DC power supply systems each configured to provide pulsed DCvoltage to a different anodeless electrode within a plasma processingchamber, each pulsed DC voltage having a selectable boost voltage duringa first portion of each pulse, and the selectable boost voltage beingdifferent for at least two of the pulsed DC power supply systems.